Online music services provide users with access to audio tracks from various artists. Such services allow users to build libraries, and to organize those libraries according to input, or predefined, preferences. For example, audio tracks in a library may be grouped into playlists. A playlist can include a set of tracks that are grouped together, either randomly or based on some commonality. A music player for use with the music service typically reads the playlist and plays the audio tracks on the playlist randomly or in some order.